is used at the time of standardising the tape
neutralizes the effect due to pull and sag
makes the correction due to sag equal to zero
makes the correction due to pull equal to zero
line ranger
steel tape
optical square
cross staff
straightening the links
removing one or more small circular rings
closing the joints of the rings if opened out
all of the above
±2 mm
±3 mm
±5 mm
±8 mm
is lighter than chain
is easier to handle
is practically inextensible and is not liable to kinks when in use
can be easily repaired in the field